Diets Closely Monitored

In the study, 19 obese adult volunteers stayed
in a metabolic ward for a pair of two-week periods. During that time, food intake
was closely monitored and controlled.

At the end of the two dieting periods,
body fat loss was greater when dietary fat was restricted compared with
carbohydrate restriction, even though more fat was burned with the low-carb
diet.

Study researcher Kevin Hall, Ph.D., who
is also a metabolism researcher at the National Institute of Diabetes and
Digestive and Kidney Diseases, has been using data from dozens of controlled
feeding studies since 2003 to build mathematical models of how different
nutrients affect human metabolism and body weight.

Hall said this study shows there are
small differences between fat and carbohydrate restriction under controlled
conditions.

That goes against the concept that all
calories are equal when it comes to body fat loss.

Are the Results Significant?

Dr. Frank Hu, Ph.D., professor of nutrition
and epidemiology at Harvard T.H. Chan School of Public Health, thinks there are
more important factors for weight loss.

While calling the study interesting and “rigorously
conducted,” Hu said it “doesn't really portray real life situations.”

“This was a small study and it was done
[under] controlled lab conditions. It doesn't necessarily apply to the way
people live,” said Hu, who is also a professor of medicine at Harvard Medical
School. “In real life, people make choices and don't always adhere to a diet
that fosters weight loss over the long run.”

In real life, people make choices and don't always adhere to a diet that fosters weight loss over the long run.

Dr. Frank Hu, Ph.D., Harvard T.H. Chan School of Public Health

Furthermore, Hu said a study that lasts
only a few weeks might not produce a complete picture and confirm whether one
diet is more beneficial than the other for long-term weight control.

“Clinical trials that have been published
so far show that, in the short term, almost all diets can lead to weight loss,”
he noted.

But the question is whether an individual
can maintain the weight loss in the long run and that primarily depends upon other
factors like behavior, he noted.

Should You Change Your Diet?

The answer isn’t that simple.

“It's important that people don't come
away with the message that this study shows that low-fat diets are better than
low-carb diets for fat loss in the real world. We tried to be very clear about
that in the paper,” Hall said.

Rather, the study attempted to understand
how the body adapts when people experience significant changes in their diets,
he explained.

Other factors, like picking a diet that
you can stick to, are far more important Hall noted.

Don't feel you're at a disadvantage because of a popular theory that low-carb diets offer some sort of metabolic advantage. Do what you can actually stick to.

Kevin Hall, Ph.D., National Institute of Diabetes and Digestive and Kidney Diseases

Hall's ultimate advice: Go with what
works best for you.

“If you think a low-carb diet is going to
give you some sort of metabolic advantage for losing fat, this study shows this
is probably not true. But if you think you can better stick to a low-carb than
a low-fat diet, more power to you,” he said.

“Don't feel you're at a disadvantage
because of a popular theory that low-carb diets offer some sort of metabolic
advantage. Do what you can actually stick to.”

Next Hall and his associates will
investigate how reduced-carbohydrate and reduced-fat diets affect the brain's
reward circuitry as well as its response to food stimuli. He hopes these
results might uncover why people respond differently to different diets.